1. Field of the Invention
The present invention relates to an apparatus for measuring a weight and/or a force caused by a substance which is subjected to severe circumstances.
2. Related Art Statement
Upon measuring a weight of a substance, an electronic weighing apparatus has been widely used. In general, a substance whose weight is to be measured is placed in a same environment as that in which an electronic weighing apparatus is installed. However, in some cases, substances are placed in severe environments such as poisonous gas atmospheres and corrosive gas atmosphere. In such a case, when the electronic weighing apparatus is installed in the same environment as that in which the substance whose weight is to be measured, the weighing apparatus and a measuring sensor are also subjected to the severe environment and are liable to be damaged. When the electronic weighing apparatus is kept in such a severe environment for a long time, the apparatus might be corroded or broken and the accurate measurement could not be carried out any more.
In order to mitigate the above mentioned problem, there has been proposed a known weight/force measuring apparatus, in which a part of an electronic weighing apparatus is placed in a substance space in which a substance is existent, and the remaining parts of the weighing apparatus are installed in a measuring space which is completely separated from the substance space. For instance, a permanent magnet is coupled with a member which is moved up and down in response to a weight of a substance and is placed in the substrate space, and a position sensor which detects a position of the permanent magnet and an electromagnetic coil within which said permanent magnet is inserted are installed within the measuring space which is separated from the substance space by means of a partition wall. In such a weight measuring apparatus, a position of the permanent magnet is detected by the position sensor and an electric current passing through the electromagnetic coil is controlled in accordance with an output signal of the position sensor such that the permanent magnet is always positioned at a predetermined position with respect to the electromagnetic coil. In this manner, a weight of the substance can be measured by monitoring the electric current passing through the electromagnetic coil.
In this known weight measuring apparatus, since almost all parts except for the permanent magnet is arranged within the safe measuring space, even if the substance space is subjected to severe conditions, the measuring could be performed. However, the permanent magnet is not directly coupled with the electromagnetic coil, but is separated from the main parts of the measuring apparatus, and therefore an accurate measurement could not be attained.